1. Field of INVENTION
The present invention relates generally to a control system for adjusting driving torque to be exerted on an automotive driving wheel for preventing the latter from causing wheel slip which is otherwise caused due to loss of road traction. More specifically, the invention relates to a slip suppressive drive control system which can reduce power output of an automotive internal combustion engine in response to excessive wheel slippage for recovery of road traction of wheel.
2. Description of the Background Art
One typical construction of a slip control system for adjusting driving torque to be applied to a road wheel, has been disclosed in Japanese Patent First (unexamined) Publication (Tokkai) Showa 58-38347. The disclosed slip control system derives a wheel slippage on the basis of difference of rotation speed of driving and driven wheels. The slip control system performs fuel cut-off for reducing engine output when wheel slippage is detected.
In such type of slip control, hunting in slip control fuel cut-off mode and normal fuel supply mode tends to be caused in certain vehicle driving conditions. Namely, when wheel slippage is caused, fuel cut-off mode operation is performed. The fuel supply system is maintained in a fuel cut-off mode while wheel slippage is greater than a predetermined wheel slippage threshold. As soon as wheel slippage drops below the wheel slippage threshold, the fuel supply system is switched into a fuel supply mode. By this engine output is instantly resumed to exert driving torque on the road wheel. This again causes wheel slippage greater than the wheel slippage threshold. By repeating fuel cut-off and fuel resumption, jerking of a vehicular body is caused to degrade vehicle riding comfort.
On the other hand, Japanese Patent First Publication (Tokkai) Showa 58-202142 discloses another type slip control system, in which a brake is applied to decelerate the road wheel in response to wheel slippage. In such system, a pressurized medium, such as pressurized brake fluid, is required to be constantly supplied. For this purpose, the system is required to have a pressure medium source which is maintained in operation while the vehicle is driven. This clearly increase the cost for facilitating the system.
Japanese Patent First Publication (Tokkai) Showa 59-18251 discloses a still another type of slip control system, in which a throttle valve angular position is adjusted for adjusting driving torque to be exerted on the road wheel. In this system, the throttle open angle is reduced in response to the wheel slippage for reducing engine load and thereby reducing the engine output. In order to achieve satisfactorily quick response in response to the wheel slippage, it is required to have a precise and high response actuator in place of the conventional mechanical linkage system, for achieving quick response in adjustment of the throttle valve angular position. This clearly causes a high cost.
Because of the defects set forth above, the prior proposed slip control systems are not satisfactory for successfully adjusting the driving torque to be exerted on the road wheel.